Actions of rab3 effector domain peptides in chief cells from guinea
pig stomach.
Singh, Gurcharn, Robert D. Raffaniello, John Eng, and Jean-Pierre
Raufman.
Gastrointestinal Cell Biology Laboratory, Department of Medicine,
State University of New York-Health Science Center at Brooklyn, 450
Clarkson Avenue-Box 1196, Brooklyn, New York 11203-2098
APStracts 2:0098G, 1995.
Rab3 proteins are low molecular weight guanine nucleotide binding
-proteins that belong to the ras superfamily and are believed to play
a role in the final steps of exocytosis. To examine potential
interactions of these proteins with signaling pathways that mediate
pepsinogen secretion from gastric chief cells, we synthesized
peptides corresponding to the effector domain of rab3. In the absence
of added calcium ([Ca2+], < 1 nM), a maximal concen- tration (15
[mu]M) of the rab3 effector domain peptide or rab3AL peptide,
containing alanine and leucine substitutions, stimulated the release
of 62 and 66%, respectively, of total pepsinogen from streptolysin O
-permeabilized chief cells. A rab2AL peptide, corresponding to the
rab2 effector domain, and modified (scrambled and truncated) rab3AL
peptides did not alter secretion from permeabilized cells. An
additive secretory response was observed when 5 [mu]M rab3AL peptide
was combined with increasing calcium ([Ca2+], < 1 nM to 3 [mu]M).
In contrast, adding up to 3 mM cAMP had no effect on rab3AL peptide
-induced secretion and rab3AL peptide did not alter endogenous cAMP
production. The addition of a non-hydrolyzable GTP analogue (0.01 to
100 [mu]M GTP[gamma]S) potentiated the secretory response to rab3AL
peptide. This potentiated response indicates that other GTP-binding
proteins are involved in calcium-independent secretion. Preincubation
of cells with streptolysin O (10 to 30 min), to allow egress of
cytosolic constituents, enhanced the response to rab3AL peptide,
suggesting that the target(s) for this peptide is(are) anchored to
chief cell membranes. In summary, rab3 effector domain peptides
stimulate exocytosis from gastric chief cells in a specific, dose
-dependent manner that is independent of changes in cellular
mediators, like calcium and cAMP. Moreover, these results suggest
that, in gastric chief cells, the effector domain regions of rab3
proteins may regulate pepsinogen secretion by interacting with
membrane-associated target molecules.
Received 27 June 1994; accepted in final form 15 April 1995.
APS Manuscript Number G242-4.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 26 May 1995.